Stair-Climbing Breaks for Prediabetes Improvement

Inclusion Criteria: Age 18 to 69 years, inclusive. Body mass index (BMI) 25.0 to 40.0 kg/m², inclusive. Objectively confirmed prediabetes based on at least one of the following: * HbA1c 5.7% to 6.4%; * fasting plasma glucose 100 to 125 mg/dL; or * 2-hour plasma glucose 140 to 199 mg/dL during a 75-g oral glucose tolerance test. Able to understand study procedures and provide written informed consent in English. Able to safely perform repeated walking and vigorous stair-climbing activity based on medical history, resting vital signs, PAR-Q+ responses, investigator assessment, and medical clearance when required. Able to safely undergo repeated venous blood collection and IV-catheter placement. Able to safely consume the standardized study meals. Willing and able to complete all three experimental conditions and comply with fasting, dietary, physical-activity, medication, and pre-visit standardization instructions. Exclusion Criteria: BMI below 25.0 kg/m² or above 40.0 kg/m². Diagnosed type 1 or type 2 diabetes mellitus. Laboratory findings that do not confirm prediabetes or that suggest diabetes, including HbA1c ≥6.5%, fasting plasma glucose ≥126 mg/dL, or 2-hour plasma glucose ≥200 mg/dL during a 75-g oral glucose tolerance test. Cardiovascular, pulmonary, musculoskeletal, neurological, or other medical conditions that would preclude safe participation in the walking or stair-climbing interventions. Resting vital signs, current symptoms, or other screening findings indicating that exercise participation would be unsafe. Pregnancy, plans to become pregnant during the study period, or breastfeeding. Current use of medications that may substantially affect glucose metabolism, lipid metabolism, body weight, study outcomes, or safe participation, including insulin, glucose-lowering medications, GLP-1 receptor agonists, pharmacologic weight-loss medications, systemic corticosteroids, or other medications judged by the investigator to interfere with study outcomes or safety. Contraindications to vascular ultrasound, repeated blood collection, IV-catheter placement, or exercise participation. Food allergies, intolerances, or dietary restrictions that prevent safe consumption of the standardized study meals. Known allergy or severe skin sensitivity to adhesives used with continuous glucose monitors. Bleeding disorder, current anticoagulant use, history of anemia, recent blood donation, recurrent fainting during blood collection, difficult venous access, or another condition judged to create unacceptable risk from repeated blood sampling or IV-catheter placement. Inability to safely perform repeated walking or stair climbing. PAR-Q+ result requiring further medical evaluation when the participant does not obtain required written medical clearance. Any other condition or finding that, in the judgment of the Principal Investigator or qualified study investigator, would make participation unsafe or substantially interfere with completion of study procedures.